Best Greek Language Lessons In Athens?

I have moved to Athens but do not speak any Greek. My work is with other English people so there is no opportunity to learn though work, and most of my other activity is with English speakers.

I desperately want to learn to speak Greek.

Can anyone recommend a good Modern Greek Language School? (Or teacher?)

Preferably based in (or close) to Syntagma, or the Glyfada area.